Induction of pyruvate dehydrogenase in 3T3-L1 cells during differentiation

The activity of the pyruvate dehydrogenase complex and the content and turnover of the pyruvate dehydrogenase component were measured during the differentiation of 3T3-L1 preadipocytes into 3T3-L1 adipocytes. The specific activity of "total" pyruvate dehydrogenase complex increased approximately 7-fold in 3T3-L1 adipocytes differentiated with a treatment of insulin plus dexamethasone plus 1-methyl-3-isobutyl xanthine. The ratio of "active" pyruvate dehydrogenase complex to total pyruvate dehydrogenase complex remained unaltered in both 3T3-L1 preadipocytes and adipocytes. A specific goat antibody to bovine kidney pyruvate dehydrogenase quantitatively precipitated both alpha and beta subunits of pyruvate dehydrogenase from solubilized 3T3-L1 adipocytes. Using immunoprecipitation and gel electrophoresis techniques, we demonstrated an approximate 6-fold increase in pyruvate dehydrogenase content in 3T3-L1 adipocytes as compared to 3T3-L1 preadipocytes. Pulse labeling experiments revealed an approximately 5-fold increase in the rates of synthesis of both alpha and beta subunits of pyruvate dehydrogenase in 3T3-L1 adipocytes after 6 days of the hormonal treatment compared to those observed in 3T3-L1 preadipocytes. In contrast, the half-lives of alpha and beta subunits of pyruvate dehydrogenase were not significantly altered in 3T3-L1 preadipocytes (41 h) and adipocytes (49 h). The 6-8-fold increment in the specific activity of the pyruvate dehydrogenase complex in 3T3-L1 adipocytes therefore results from increased rates of synthesis of alpha and beta subunits of pyruvate dehydrogenase.